Cutting and abrading tools



c; H. Boom CUTTING AND ABRADING TOOLS "may 17, 1955 2,708,376

Original Filed Nov. 7, 1949 M Nlnvewtar Z2 ch'r a vherfi'sonwotb UnitedStates Patent 0 cUrrrNG AND ABRADING TOOLS Christopher Hodgson Booth,Bath, England, assignor to Firth-Brown Tools Limited, Shefield, England,a British company Original application November 7, 1949, Serial No.12653-32. Divided this application September 14, 1953, Serial No.379,892

Claims pricrity, application Great Britain November 8, 1948 6 Clm'ms.(Cl. 7624) The invention relates to cutting and abrading tools of thekind having a large number of cutting edges upstanding from the face ofthe tool and exemplified by files, rasps, and abrading bands and discs.It is an object of the invention to provide for use in tools of thiskind new or improved cutting elements in which the cutting edges areformed on thin strip or sheet material, tools employing such elementsand a method of making the elements.

The invention is based on the appreciation that in such tools the depthof cut by each individual cutting edge is very small and accordinglythat, provided the chips or swarf may be cleared from the cutting edge,the depth of the edge may be correspondingly small. Further the pressureon each cutting edge is small and the body of the tool need only havesufiicient strength and rigidity to support the edge and apply thenecessary small cutting pressure. On the other hand it is important thatthe edge should be sharp to enable it to bite into the material andremove by cutting, the thin chip resulting from the small depth of cut.

Cutting or abrading tools which consist of a sheet of tin-plate or thelike comparatively soft material having a multiplicity of abrading edgesformed by striking out from the surface of the sheet parts of theperipheral edges of holes formed in the sheet and which are usually usedfor culinary purposes, are well known. The principle of providingcutting edges by striking out parts of the peripheries of holes in sheetmaterial is employed in the present invention.

The invention provides the method of producing hardened cutting edges onthe surface of a strip or sheet of thin flexible steel or otherhardenable iron alloy to be used in or as a cutting tool, which methodcomprises the steps of striking out a multiplicity of portions of thestrip or sheet material from the surface thereof to an extent at leastequal to the thickness of the material and to make 1 an acute angle withthat surface, wholly or partly removing (e. g. by grinding down) thestruck-out portions thereby to produce sharpened edges on the materialat the peripheries of the holes therein, setting the sharpened edges toproject from the general plane of the material and hardening the edgesdifierentially with respect to the body of the material.

In the preferred form of the method the struck-out portions are removedas aforesaid by grinding and the heat developed during the grindingoperation is employed to effect the hardening of the cutting edges.

Some specific examples of cutting elements, of tools formed from theelements, and a method of manufacturing the elements will now bedescribed with reference to the accompanying drawings which are to someextent diagrammatic and in which:

Figure 1 represents a portion of a cutting strip,

Figure 2 is an enlarged view of a part of the strip,

Figure 3 is a section on the line 3-3 in Figure 2,

Figure 4 is a section on the line 44 in Figure 2,

Figure 5 is a diagram illustrating the theoretical shape of one of thecutting edges,

- included C1 angle of about 30.

Figure 6 is a section showing an alternative form of strip havingcutting edges on both sides,

Figure 7 is a view showing another form of cutting edge,

Figure 8 is a section on the line 88 in Figure 7, Figures 9-11illustrate three stages in the formation of the cutting edges employedin the construction shown in Figures 1-4.

The cutting strip illustrated in Figure 1 consists of a strip of sheetsteel having in this example, a thickness of between 0.003 and inch. Thestrip is formed with a multiplicity of D-shaped holes 1, which arearranged in V-shaped or chevron shaped rows, the holes in one row beingstaggered in relation to the holes in adjacent rows. The length of thestraight edge of each hole is about 0.10 inch, adjacent holes in eachrow are pitched at approximately 0.175 inch apart, and the rows arepitched at approximately 0.175 inch apart. The straight edge of eachhole is sharpened, hardened and set in the manner about to be described,to form a cutting edge and it will be understood that with the staggeredarrangement of the rows and holes just described the edges in adjacentrows combine to provide in effect continuous cutting edges.

Figures 2-5 show in greater detail the form of the cutting edges. Eachedge 2 has a clearance angle A relative to the surface 3 of the strip,an angle of rake B and an included angle C. Further, the extent by whichthe edge 2 set to project from the surface of the strip 3-increases fromnil at the ends of the edge to about 0.0l5 of an inch at the centre. Theextent of the projection will be varied for different uses to which thetool is to be put and may be more or less (e. g. 0.003 to 0.005 inch)than the height of 0.015 inch mentioned. In every case the height willbe small. It will be seen from Figures 3 and 5 that the extent of theupset of the edge determines the depth of the out which can be made,this depth being limited by the body of the strip engaging the workahead of the edge. Figure 3 shows the cutting edges in operation on aworkpiece 5 and it will be noticed that the chips 6 are directed throughthe holes 1.

Figure 6 shows a modified form of the strip in which cutting edges 2 areprovided on both faces of the strip.

Figures 7 and 8 show an arrangement in which the holes la are ofcircular form and countersunk at an Over rather less than half thecircumference of the hole the edge is set to project from the strip toform a cutting edge 2a, the extent of the projection increasing, as inthe previous example, from nil at the ends to a few thousandths of aninch at the centre of the edge.

- It is important that in every case the holes 1 should be of a size andshape to permit free passage of the cutting produced by the cutting edgeand it may, sometimes, be desirable to vary the size of the holesaccording to the material which the tool is constructed to cut.

Figures 9-11 illustrate one method of forming on spring hardened steelstrip or sheet material sharpened edges such as those shown in Figures1-5. he first step in the formation of the edges is to strike out, bymeans of suitable punches and dies, D-shaped tongues 10 from the surfaceof the strip or sheet. The extent to which the free edge of each tongueis struck out is greater than the thickness of the material so that theedge 11 and the whole and preferably only the whole, of thesemi-circular end of the tongue projects from the surface of thematerial. The tongue makes an angle with the surface of the materialwhich is the desired included angle of the cutting edge. The next stepin the method is to grind oil the portion of the tongue which is abovethe surface of the material thereby leaving a straight sharp edge 12 asshown in Figure 10. The rate of grinding and the other conditions of thegrinding operation, including the rate of cooling the material, are sodetermined that the heat developed in the material is suthcient toharden the edge 12 but not substantially to afiect the body of thematerial. The next step is to set the edge 12 to constitute the cuttingedge 2 as shown in Figure 11, the edge also being shaped as shown inFigure 4. The edges may be set by the use of suitable punches and diesand registration of the edges with the setting means may be effected bylocating pins fitting into holes adjacent to those being treated. Tocomplete the method the edges may be sandblasted to effect a finalsharpening or they may be sharpened in any other suitable way. For somepurposes this final step will not be necessary. if the method is to beapplied to the production of edges on both sides of a sheet or stripasshown in Figure 6, the tongues are first struck out in opposeddirections from a straight dividing line, the ends of the tongues beingsquare in this case, and the operation or" grinding and setting arecarried out on both sides of the sheet or strip.

The angles of clearance and rake of the edges will be varied to suit thematerial on which the tool is intended to be used and will, in general,be about the same as the corresponding angles employed in a single pointcutting tool to be used on the same material although the angles whichmay be employed in the present invention are not limited to those whichmay be employed in a single tool 7 because the latter are governed to agreater extent by clearance angle would be about 10 and the includedangle 4550 and for harder metals the clearance angle would be about 7and the included angle 65-70". shear angle may be varied as isconvenient.

I claim: 7

l'. The method of forming hardened cutting edges up- 7 standing from thesurface of a piece of thin flexible hardenable-steelsheet, which methodcomprises the steps of Y t striking out from the sheet a multiplicity ofportions thereof all extending at, acute angles with the surface of thesheet in the same general direction and the portions being The struckout at least to the extent that one face of a part of each portion isbrought beyond the level of the opposite face of the body of the sheetand the thickness of the said part lies outside the thickness of thesheet, removing the material of said part which lies outside of a planewhich is parallel to'the surface of the sheet and intersects the firstmentioned face, thereby to produce for each struckout portion a sharpedge at the intersection of said plane and face and at the periphery ofa hole in the sheet, setting the edges to project with clearance anglesfrom the general plane of said sheet and hardening the edgesdifiereutially with respect to the body of the sheet.

2. The method according to claim 1 in which the material is heated andcooled subsequently to the aforesaid removing operation to effect thehardening of the edges.

3. The method according to claim 1 in which the portions struck out arein the form of tongues.

4. The method according to claim '1 in which the edges are set asaforesaid with positive rake angles relative to the general plane of thesaid sheet.

'5. The method of forming hardened cutting edges upstanding from thesurface of a piece of thin flexible hardenable-steel sheet, which methodcomprises the steps of striking out from the sheet a multiplicity ofportions thereof all extending at acute angles with the surface of thesheet in the same general direction and being struck I out to the extentthat one face of a part of each portion is brought at least to the levelof the opposite face of the.

hole in the sheet, setting the said edges to project from the generalplane of the sheet and hardening the edges differentially with respectto the body of the sheet.

6. The method according to claim 5 in which the edges are set asaforesaid with angles of clearance and rake 7 relative to the generalplane ofthe said sheet.

References Cited in the file of this patent UNITED STATES PATENTS974,099 Sundborg Oct. 275, 1910 FOREIGN PATENTS Great Britain Feb. 22,1909

